The present invention relates to a temperature control system for process chambers.
In the fabrication of devices for electronic applications, semiconductor, dielectric and conductor materials, such as for example, polysilicon, silicon dioxide, and metal containing layers, are deposited on a substrate and etched to form features such as gates, vias, contact holes and interconnect lines. These features are typically formed by chemical vapor deposition (CVD), physical vapor deposition (PVD), oxidation and etching processes. For example, in a typical etching process, a patterned mask of photoresist or oxide hard mask is formed on a deposited layer by photolithographic methods and exposed portions of the deposited layer are etched by an energized halogen gas, such as Cl.sub.2, HBr and BCl.sub.3. In a typical CVD process, a gas provided in the chamber is decomposed to deposit a layer on the substrate. In PVD processes, a target facing the substrate is sputtered to deposit the target material onto the substrate. In all of these processes, the substrate is transported into a process chamber, a desired composition of process gas is introduced into a chamber, and plasma is formed from the process gas by energizing an inductor antenna or electrodes to process the substrate.
Temperature control systems are used to control the temperatures of the process chambers because the deposition and etching processes are often highly temperature dependent. For example, in etching processes, the shape of the etched features is often dependent upon process temperature which can change across the substrate surface. In CVD and PVD processes, the rate of deposition of material is highly dependent upon the temperature of the substrate. Another problem arises from the residues formed on chamber surfaces, which flake off and contaminate the substrate when subjected to thermal stresses arising from changing temperatures that occur when, for example, the plasma is de-energized during transport of the substrate in and out of the chamber. Thus, it is desirable to control the temperature of the chamber surfaces and reduce temperature fluctuations from one process cycle to another.
Conventional temperature control systems include water-jacket recirculating systems and forced-air cooling systems. Water-jacket systems recirculate water through cooling channels that surround the chamber. However, the cooling channels occupy valuable space around the chamber that is often needed for placement of other external components. Also, because both the cooling fluid itself and the metal channel can absorb RF energy, it is difficult to place and position the channels around a chamber that has inductor coils for coupling inductive energy into the chamber. The presence of inductor coils render it difficult to control the temperature of an underlying or adjacent chamber surface. In addition, because the cooling channel has to circumvent around the external components, localized hot spots often occur at locations bypassed by the cooling channels. It is also difficult to obtain uniform heat transfer rates across the chamber because the cooling channels are hard to attach to complex shaped or convoluted chamber surfaces.
Forced air cooling systems, such as those described in U.S. Pat. No. 5,160,545, issued Nov. 3, 1992, which is incorporated herein by reference, typically use a fan to blow air across the chamber surfaces and through a heat exchanger for cooling. However, portions of the chamber surface that are shielded from the cooling air by components become hotter than other unshielded portions, as for example, described in the background of U.S. patent application Ser. No. 09/057,097 to Kholodenko et al. entitled "Temperature Control System for Semiconductor Process Chamber," filed Apr. 8, 1998, now U.S. Pat. No. 6,015,465, which is incorporated herein by reference. Kholodenko et al. also state that because the primary mode of heat transfer is conduction through contact with gas molecules, forced air systems require large flow rates to control large temperature fluctuations, such as the temperature changes caused by turning on and off the plasma or other heat loads. Kholodenko et al. further state that large air flow rates require large fans which upon failure can severely damage other components present around the fan.
For example, a typical forced air conventional system 2 for controlling the temperature of a process chamber 3 is shown in FIG. 1. In this system, heat lamps 4 maintain the temperature stable during idle and run modes, and the plasma generated during a process run mode provides a further heat load that results in a large temperature fluctuation of the chamber surfaces 5. The plasma heat load is partially dissipated by an overhead fan 6 that is enclosed by a housing 7 and that blows recirculated air onto the surface 5 of the chamber 3. Generally, air flows down across the surface 5 of the chamber 3 up an annular passageway 9 defined by an inner wall 10 and the sides 11 of the housing which includes a heat exchanger 12 formed by cooling coils. The cooled air then re-enters the fan 6 from the sides of the fan blades 13. However, such a forced air system 2 has a cooling ability and response time that is limited to the volumetric flow capacity of the fan 6. In addition, the mechanical vibrations of the fan 6 can cause flaking of deposits formed on the chamber surfaces 5 or movement of the underlying substrate, both of which are undesirable. Furthermore, recirculating air within the enclosed environment has a constant heat load that is difficult to rapidly dissipate.
Thus, despite extensive work over many years, there remains a need for an improved system for controlling the temperatures across a process chamber. It is desirable to have a temperature control system capable of maintaining the surfaces and walls of the process chamber at uniform and stable temperatures even for changing heat loads applied to the chamber. It is also desirable to have a temperature control system that does not absorb RF energy from components such as an inductor antenna.